The Trace Element Selenium Is Important for Redox Signaling in Phorbol Ester-Differentiated THP-1 Macrophages

Physiological selenium (Se) levels counteract excessive inflammation, with selenoproteins shaping the immunoregulatory cytokine and lipid mediator profile. How exactly differentiation of monocytes into macrophages influences the expression of the selenoproteome in concert with the Se supply remains obscure. THP-1 monocytes were differentiated with phorbol 12-myristate 13-acetate (PMA) into macrophages and (i) the expression of selenoproteins, (ii) differentiation markers, (iii) the activity of NF-κB and NRF2, as well as (iv) lipid mediator profiles were analyzed. Se and differentiation affected the expression of selenoproteins in a heterogeneous manner. GPX4 expression was substantially decreased during differentiation, whereas GPX1 was not affected. Moreover, Se increased the expression of selenoproteins H and F, which was further enhanced by differentiation for selenoprotein F and diminished for selenoprotein H. Notably, LPS-induced expression of NF-κB target genes was facilitated by Se, as was the release of COX- and LOX-derived lipid mediators and substrates required for lipid mediator biosynthesis. This included TXB2, TXB3, 15-HETE, and 12-HEPE, as well as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Our results indicate that Se enables macrophages to accurately adjust redox-dependent signaling and thereby modulate downstream lipid mediator profiles.

Chemical Elements in Electronic Cigarette Solvents and Aerosols Inhibit Mitochondrial Reductases and Induce Oxidative Stress

Introduction Chemical elements and their toxicity were evaluated in electronic cigarette (EC) solvents, fluids, and aerosols. Aims and Methods Element identification and quantification in propylene glycol (PG), glycerin (G), refill fluids before and after use, and aerosols was done using inductively coupled plasma optical emission spectrometry. Cytotoxicity and oxidative stress were evaluated using in vitro assays. Results Seven elements were present in PG, G, and popular refill fluids, and they transferred to aerosols made with ECs. Selenium was in all products (0.125–0.292 mg/L), while arsenic, aluminum, and tin were frequently in solvent and refill fluid samples at lower concentrations. Iron, chromium, copper, nickel, zinc, and lead were only detected in fluid after EC use, indicating they came from heated atomizers. Elements transferred most efficiently to aerosols made with second-/third-generation ECs. Of the elements in fluid, selenium and arsenic were the most cytotoxic to human bronchial epithelial cells (BEAS-2B) and pulmonary fibroblasts in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium increased superoxide production in mitochondria and nucleoli and elevated selenoprotein H in nucleoli of BEAS-2B cells at concentrations found in EC aerosols (10 nM or 0.002 mg/L). Conclusions Elements in EC aerosols came from both e-fluids and atomizing units. Within second-/third-generation products, transfer became more efficient as power increased. In vitro responses occurred at concentrations of selenium found in some EC aerosols. Human exposure to chemical elements in ECs could be reduced by regulating (decreasing) allowable EC power and by improving the purity of PG and G. Implications PG, G, refill fluids, and e-fluids contained potentially toxic chemical elements that transferred to aerosols. Transfer was more efficient in second- and third-generation EC products and increased as power increased. Selenium and arsenic were the most cytotoxic of the elements tested in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium tetrachloride-induced oxidative stress in BEAS-2B cells, but not in human pulmonary fibroblasts. All fluids contained selenium above the concentration that induced oxidative stress in human bronchial epithelial cells. Selenium increased superoxide in mitochondria and nucleoli and increased selenoprotein H, a redox responsive DNA-binding protein that is upregulated by superoxide and an indicator of nucleolar stress. EC users are exposed to elements in aerosols, which may with chronic exposure contribute to diseases associated with oxidative stress.

Selenium Status Influences Selenoprotein H Interactions with Other Selenoproteins in the Response to Oxidative Stress (P24-026-19)

Objectives Selenium (Se) is an essential trace element exerting its biological functions mainly through selenoproteins. Evidence suggests that selenoprotein H (SELONOH), a nuclear protein against oxidative stress and cellular senescence, is the most prominent selenoprotein that responds in parallel to dietary Se deficiency and age in telomere-humanized mice displaying type-2 diabetes-like symptoms. On the other hand, SELENOH is one of the few low-hierarchy selenoproteins whose expression is very sensitive to fluctuations in Se status. The objective of this study was to explore impacts of SELENOH on the expression of other selenoproteins and redox regulation upon changes in Se status. Methods A plasmids expressing wild-type SELENOH was constructed and transfected into human HEK293T cells, followed by analyses of Se status and cellular functions. Results Adding Se (Na2SeO3, 0–200 nM) to cell culture medium dose-dependently increased protein levels of overexpressed SELENOH and other selenoproteins including glutathione peroxide 1 and thioredoxin reductase 1; however, their mRNA transcripts were not affected by Se status. Overexpressed SELENOH suppressed protein expression of these two selenoproteins. Supplementing Se (100 nM) enabled overexpressed SELENOH to protect against paraquat-induced senescence and slow proliferation. Analyses of SELENOH-associated proteins through LC-MS-MS co-identified nucleolar and glycosylation proteins. Conclusions Altogether, these results suggest that SELENOH could compete with other selenoproteins for available Se but protects against oxidative stress together with them. Funding Sources NIH.

Modern concept of biological identification of selenoproteins

Humans possess 25 selenoproteins, approximately half of which are enzymes (selenoenzymes) required for preventing, regulating, or reversing oxidative damage, while others participate in providing calcium metabolism, thyroid hormone maintenance, protein synthesis, cytoskeletal structure etc. This review examines the latest evidences of the biological effects of selenoproteins according to the method of complex analysis of the material. Selenoprotein P promotes insulin resistance in type 2 diabetes, mediates myocardial ischemic-reperfusion injuries and provides protection against disease by reducing chronic oxidative stress. Selenoprotein T is expressed at the endoplasmic reticulum membrane in all cells during development, but is confined to endocrine tissues in adulthood, controls homeostasis of glucose and prevents neurodegeneration by reducing oxidative stress factors. Expression of selenoprotein K is required for efficient Ca2+ flux into melanoma cancer cells, tumour growth and metastasic potential depend on SelK but it suppresses human choriocarcinoma cells. SelK also serves to maintain the normal physiological functions of skeletal muscle. Selenoprotein N deficiency, caused by mutations in the human gene, promotes myopathy characterized by muscle weakness, spinal rigidity, respiratory insufficiency. Sel N participates in normal physiology of skeletal and smooth muscle tissues. Selenoprotein M is located in the endoplasmic reticulum, characterized by high expression in the brain, antioxidative, neuroprotective activity and regulates intracellular Ca2+ levels. Also, the overexpression of SelM was detected in human hepatocellular carcinoma. Selenoprotein S is mentioned as a regulator of ER stress and inflammatory processes. Selenoprotein F controls cell proliferation by the impact on G1period of the cell cycle. Moreover, it is implicated in the pathogenesis of some types of cancer. The Sel F deficiency reduces the migration and invasive ability of the cells. Knockdown of selenoprotein W in rodents leads to increased release of Ca2+, causes oxidative ultramicroscopic injuries of the endoplasmic reticulum and mitochondria ultrastructure, which in turn increases the levels of inflammatory factors. Selenoprotein H is involved in redox regulation, in tumourogenesis. Knockdown of selenoprotein H decreases cellular differentiation and increases proliferation and migration of cells. Selenoproteins U, V, I, O, R are recently identified and their functions are not clearly known. The data analyzed in the review help determine promising directions in the study of the selenoproteins.